1. Field of the Invention
The present invention relates to disk apparatuses for controlling a head such that the head seeks information at the center of the target track on a disk, such as a floppy disk (FD), during a reproduction operation.
2. Description of the Related Art
In a conventional floppy-disk drive apparatus, a step driving mechanism employing a stepper motor is used as a head feed unit for moving a head to a track where recording is to be performed concentrically on a recording plane of a disk. With a mechanical step operation of this head feed unit, the head is positioned at the track. Instead of the step driving mechanism, a head feed unit having a linear-motor (voice-coil motor: VCM) drive is provided for some floppy-disk drive apparatuses to move the head continuously.
In a disk apparatus of such a type, a head-position detection unit detects a return of the head to the origin and reports it to the host computer. To move the head to the target track of a disk, the host computer sends seek instruction-pulses, one for one track, to the disk apparatus. According to this seek instruction pulses, the disk apparatus moves the head by the number of tracks corresponding to the seek instruction pulses.
In apparatuses such as the conventional floppy-disk drive apparatus, a screw shaft driven by a stepper motor is engaged with a head base and the head is fed by the rotation of the screw shaft. Since the mechanical connection determines the relationship between the rotation of the stepper motor and the movement position of the head, the head is moved to the target track just by driving the stepper motor according to the seek instruction pulses sent from the host computer.
On the other hand, in apparatuses employing a head feed unit having a linear-motor drive, since a head base has movement flexibility in the head feed unit, a head-position detection unit for always detecting the movement position of the head and a head-position control unit using the detection output thereof need to be provided.
Such a head feed unit having a linear-motor drive is, for example, included in a disk apparatus in which a high-density-recording disk on which a servo signal is recorded for tracking and a floppy disk (FD) having a capacity of 2 megabytes (MB) can be loaded. The high-density disk to be loaded into this type of a disk apparatus is also a flexible disk. In the following description, a flexible disk having a capacity of 2 MB is called a floppy disk and it is discriminated from the high-density disk.
When the high-density disk is loaded, the head is moved by a linear-motor drive. The head reads the servo signal and is positioned at a track. On the other hand, when a floppy disk is loaded, the head feed position is controlled according to the detection output of the head-position detection unit and the head is positioned at the track.
In the head-position detection unit, a linear scale having slits at a constant interval is provided for either the head base or a chassis, and a light source and a light-receiving device opposite each other through the slits are provided for the other part. According to the movement of the head, a detection output in which the polarity of the output strength is periodically changed is obtained from the light-receiving device.
For example, detection outputs having two different phases are obtained. The head-position detection unit is mounted such that the head is positioned on the center of a track recorded in the disk at the center point of the maximal value and the minimal value of a detection output.
The detection outputs corresponding to each track are measured and stored as sets of the maximal values and the minimal values in a calibration operation at a drive start. Alternatively, they are measured and stored in advance in a shipment process of the disk apparatus. When track tracking control is performed in which the head tracks the target track, the center values (hereinafter called reference center values) of the maximal values and the minimal values of the detection outputs corresponding to the target track are obtained and the VCM is driven such that the detection output signals have the reference center values. Tracking control for the target track is performed in this way.
The detection outputs of the head-position detection unit may vary due to external causes such as the variations of the surrounding temperature and of the power voltage of the disk apparatus. In other words, the detection outputs vary due to DC offsets applied to the detection outputs.
If such a DC offset occurs, the center value of the maximal value and the minimal value of a detection output is shifted from the reference center value, and as a result, the target position in the track tracking control is shifted from the actual track center.
When a disk is loaded, if the calibration operation is executed, even if the detection outputs of the head-position detection unit vary, sets of the maximal values and the minimal values of the newly detected detection outputs corresponding to each track can be used to eliminate the generated variations of the detection outputs.
In the interface corresponding to the conventional floppy disk, however, when the host computer sends a recording/reproduction request command, since it is necessary to immediately execute this command, it is undesirable that a calibration operation is performed, for example, when a disk is loaded after the disk apparatus is started. Therefore, variations of the detection outputs generated after a calibration is performed at the start substantially cannot be eliminated.
The present invention has been made to solve the foregoing drawback. Accordingly, it is an object of the present invention to provide a disk apparatus which allows the variations of the detection outputs of a head-position detection unit, caused by a change of the surrounding condition or for some reason, to be compensated for.
The foregoing object of the present invention is achieved through the provision of a disk apparatus including: a rotation driving section for rotating a disk; a head facing a recording surface of the disk; head feeding means for feeding the head in a direction in which the head traverses tracks on the disk; head-position detection means for obtaining a detection output whose signal strength has a polarity periodically changed according to the movement of the head; and a control section for controlling the head feeding means according to the detection output obtained by the head-position detection means, wherein the control section calculates an offset between a reference center value specified in advance and the center value of the maximal value and the minimal value of the detection output detected when a seek operation, in which the head is moved to a target track, is performed; calculates a compensation value to reduce or eliminate the offset; and applies compensation control to the reference center value according to the compensation value.
The disk apparatus may be configured such that the detection output in the seek operation is integrated in time with the reference center value being used as a reference, and the obtained integrated value is multiplied by a coefficient to obtain the compensation value.
The reference center value may be compensated for according to an offset between the reference center value and the center value obtained from the maximum value and the minimal value of the detection output, detected in the seek operation, preferably, the center value obtained from the averages of the detected maximal values and the detected minimal values for a plurality of waveforms.
The reference center value may be specified for each track or for each set of a plurality of tracks which can be all tracks.
It is preferred that the disk apparatus be configured such that the calculation is performed for each track or each set of a plurality of tracks and the coefficient is specified so that the offset is reduced at a predetermined rate when the head traverses a predetermined number of tracks.
When the offset is gradually compensated for in this way, if noise is mixed at a detection or a signal having an offset extremely increasing temporarily is generated, for example, the compensation value receives a reduced effect and its reliability is improved.
The disk apparatus may be configured such that the center value is obtained for each track or for each set of a plurality of tracks which can be all tracks, from the maximal value and the minimal value of the detection output corresponding to each track, detected when the head is moved at a lower speed than that in the seek operation, the center value is stored as the reference center value, and the compensation is applied to the reference center value. The set of the maximal value and the minimal value of the detection output may be that of the maximal value and the minimal value obtained for a set of a plurality of tracks.
The reference center value may be specified when the disk apparatus is manufactured, or when the user stops using the apparatus. The reference center value may be specified by the use of the integrated value, as described above.
The control section may perform track tracking control such that the reference center value corresponds to the center of the target track.
As described above, according to the present invention, when the head position is controlled by using an output of the head-position detection unit, the variation of the center value of the detection output of the head-position detection unit is compensated for and a highly precise head-position detection is allowed.